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Solar PV: Cells, Modules, System design 05/07/2022 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 1

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Page 1: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 1

Solar PV: Cells, Modules, System design

Page 2: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 2

Solar EnergyThe sun is a sphere of intensely hot gaseous matter with a diameter of 1.39 x 109 m

The sun is about 1.5 x 108 km away from earth,

as thermal radiation travels with the speed of light in a vacuum (300,000 km/s), after leaving the sun solar energy reaches our planet in 8 min and 20 s.

Page 3: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 3

Solar Irradiation•Sun is a radiating body at 6000oC•Solar power falling earth’s atmosphere is 175 PW•Max. output is in visible range (within dashed lines)•Certain wavelengths are scattered & absorbed by air, moisture & aerosols present in atmosphere.•This effect varies with thickness of atmosphere the light must penetrate called as Air Mass (AM)•When sun is directly overhead, light would pass through 1 AM. At lower angles distance might be 2 or more times. •For measurement purpose AM1.5 is the standard. Spectral Distribution of Sun

Page 4: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 4

Solar Photo voltaic Cell 1839 photovoltaic effect in selenium in 1839. Silicon PV cells developed in 1958 Solar cell is the primary device for Solar Photovoltaic Systems. Pure silicon with high

crystal quality is needed to make solar cells. To enable silicon material to generate energy, impurities, the doping atoms, are introduced into crystal lattice.

When solar cell is exposed to light, photons are absorbed by the electrons. The input of energy breaks electron bonds.

Light knocks loose electrons from silicon atoms Freed electrons have extra energy or ‘Voltage’. Internal electric field pushes electrons

to front of cell Electric current flows on to other cells or to the load. Cells never ‘Run out’ of

electrons

Page 5: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 5

Solar Photo voltaic cell Silicon solar cell comprises of two differently doped silicon layers. The layer that faces the sun’s light is negatively doped with phosphorous. The layer below is positively doped with boron.

To take power from the solar cell, metallic contacts need to be fitted on the front and back of the cell. Contacts are usually in the form of a thin grid structure. Antireflective coating of silicon nitride or titanium oxide is applied into the front face to reduce light reflection. The front layer must let the light to enter maximum possible extent.

When light falls on solar cell, charge carriers separate and current flows through load.

Page 6: Solar PV Cells, Module and Array

01/05/2023 6

Solar Photo voltaic cell Photo voltaic addition in Cells/ Modules- In each cell, electron gains about one volt

when they are energized and ionized by photons. I n passing through the p/n junction, they lose about one half volt through collisions &

accelerations, so electrons are left with only one half volt. The process continues & as a net result electrons carry one half volt all the time. Solar cells can be combined in series parallel to increase voltage and current. When cells are connected in series, the current flow through each cell is same and the

resulting voltage is the sum of the voltages of each cell. When cells are connected in parallel, the voltage across each cell is the same and

currents add to produce a final current.

IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY

Page 7: Solar PV Cells, Module and Array

01/05/2023 7

Solar Modules MODULES are produced by connecting 30-36 cells in series, which generates 15-18 volts, enough to charge a 12V battery.

Like solar cells, solar modules can also be connected in series and parallel to increase voltage & current.

For higher voltages, MODULES are interconnected to form PANEL.

PANELS are interconnected in parallel to form ARRAYS to achieve higher current.

IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY

Page 8: Solar PV Cells, Module and Array

01/05/2023 8

Solar Modules

IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY

• Series connected cells increase voltage potential

• Parallel connected cells increase current potential

Page 9: Solar PV Cells, Module and Array

01/05/2023 9

Combining Cells & Modules

IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY

Page 10: Solar PV Cells, Module and Array

01/05/2023 10

Combining Cells & Modules

IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY

Electrical parameters:Short circuit current - Isc Open circuit voltage- VocCurrent at maximum power point – Imp- Used as the rated current of the deviceVoltage at maximum power point- Vmp- Used as the rated voltage of the deviceMaximum Power (Pmax)Fill factor- It is a indication of solar panel conversion efficiency.

area Aarea B

Cell

Curr

ent

in A

Isc

Imp

Pmax

Vmp

VocCell Voltage in

V

Fill Factor =

Area B

Area A

Page 11: Solar PV Cells, Module and Array

01/05/2023 11

Effect of Light intensity

IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY

Effects of Light Intensity: Change of intensity of light changes, the number of photons entering PV devices that proportionally changes the number of electrons released. Isc is directly proportional to light intensity, and voltage varies more slowly in a logarithmic relationship. Internationally accepted standard for light intensity is 1000 watts/ m2. It is called as one SUN or peak irradiance.

Voc drops slowly with lower irradiance

Imp

Voc

Lower irradiance reduces current

I

Page 12: Solar PV Cells, Module and Array

01/05/2023 12

Effect of Temperature

IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY

Effects of Temperature: Increase in cell temperature, reduces the voltage available at most current. This change in voltage is directly proportional to temperature.Isc rises slightly as temperature goes up. The power reduction factor in maximum power is a general factor to use to estimate the effect of temperature on output power. It is generally about -0.45% to -0.5%.A standard cell temperature of 25deg c has been accepted internationally.

Higher temperature reduces voltage

I

Page 13: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 13

Solar radiation : Seasonal variation

Seasonal variation results due to two reasons1. The Earth's orbit around the Sun is not circular

but elliptical, meaning that it is closest to the Sun in late Summer and farthest away in late Winter. However, this has only a slight effect on the intensity of solar radiation.

2. More important is the axial tilt of the Earth at 23.45°.

Both variations mean that the path of the Sun through the sky changes significantly throughout the year effecting the intensity of incident solar radiation

Page 14: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 14

Solar radiation : Effect of Atmosphere

Reduction of solar radiation due to absorption, scattering and reflection in the atmosphere;Change of spectral content of the solar radiation due to greater absorption or scattering of some wavelengths;the introduction of a diffuse or indirect component into the solar radiationlocal variations in the atmosphere (such as water vapor, clouds and pollution) have additional effects on the incident power, spectrum and directionality.

Page 15: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 15

Solar radiation : Effect of Atmosphere

gasses, like ozone (O3), CO2, and H2O vapour , have very high absorption of photons having energies close to bond energies of these gases, results in troughs in the spectral radiation curveLight is absorbed as it passes through the atmosphere and at the same time it is subject to scattering (Ex Rayleigh scattering effect)Scattered light is undirected, and so it appears to be coming from any region of the sky. This light is called "diffuse" lightEffect of clouds and other local variations in the atmosphere

Page 16: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 16

THREE RULES TO GET THE BEST OUTPUT FROM SOLAR PANELS

Rule 1

There should be no shade on the panel between 09:00 and 15:00.

Rule 2

Tilt the panel at an angle equal to the latitude of the site, though it should never be tilted less than 5 degrees from horizontal. The panel should face north for sites south of the equator and it should face south for sites north of the equator.

Rule 3

Mount the panel at least 10cm above other surfaces so air can easily cool the back of the panel.

Page 17: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 17

SPV Standalone System

Page 18: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 18

Type of Solar PV Systems Simple One/ Two Module DC Systems- Rural home/ street lighting systems. Modules

connected to a simple low cost battery through a simple charge regulator.

Large DC Systems- Centralized home lighting systems. Multiple modules with higher

capacity charge controller and single deep cyclic battery used.

AC/DC Power Systems- Here additionally, DC to AC inverter is also used to operate

appliances working on AC

Page 19: Solar PV Cells, Module and Array

01/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 19

Type of Solar PV Systems SPV-Generator Hybrid Systems- These Systems are combination of photovoltaic and diesel systems and offer best that both have to offer. Such systems consist of large arrays of modules, computerized system controller, battery bank for handling load requirement and DG set etc.

Grid-Connected Systems- These systems are designed to work with grid. Solar arrays and grid, both, are connected to normal distribution box through the system controller. Excess power produced during the day time is fed into system controller and changed into pure sinusoidal AC power that is synchronized with the grid frequency.

Page 20: Solar PV Cells, Module and Array

• Interface and Control of Backup Energy Sources• Divert PV Energy to an Auxiliary Load• Serve as Wiring Centre.

Charge regulators are required to control storage & distribution of solar energy and to also protect battery from being overcharged by array & over discharged by the loads. The array is connected to batteries & loads through charge regulator. In some designs, it may also provide status information to the user. Other functions of the charge regulator and system control are as under.

Charge Regulator & System Controls

Page 21: Solar PV Cells, Module and Array

Switching Control of Charge Regulator is done at four basic control set points

Voltage regulation set point (VR) & Array Reconnect Voltage refers to the voltage set points at which the array is connected & disconnected from the battery to prevent over-charge.

The low voltage load disconnect (LVD) and load reconnect voltage (LRV) refers to the voltage set point at which load is connected or disconnected to prevent battery over-discharge.

Charge Regulator & System Controls (contd..)

Page 22: Solar PV Cells, Module and Array

Simple Series Configuration Without Over discharge Protection

With Overdischarge Protection

PV Array Charge Regulator Battery Load

Charge Regulator

Battery

LoadPV Array

Page 23: Solar PV Cells, Module and Array

Batteries used in PV Systems

Batteries are used to store the energy produced in excess during the day time and operate the load when the PV array can not supply enough power. It also allows loads to operate during extended periods of cloudy or overcast weather. Primary functions of batteries are as under.

• Energy Storage capacity and Autonomy

• Voltage & Current Stabilization

• Supply Surge Currents

Page 24: Solar PV Cells, Module and Array

Batteries used in PV Systems (Contd.)

Batteries are used to store the energy produced in excess during the day time and operate the load when the PV array can not supply enough power. It also allows loads to operate during extended periods of cloudy or overcast weather.

• The battery storage capacity is generally sized to meet daily electrical loads for specified number of days without input from PV array for a specified autonomy period i.e. days of storage. The greater the design autonomy period, the larger the battery capacity required for a given load.

Page 25: Solar PV Cells, Module and Array

Batteries used in PV Systems (Contd.)

• Voltage & Current Stabilization – Another purpose of batteries in standalone system is to stablise or level out the potential wide variations in voltage and current that may occur in PV system. Battery also allow the loads to operate within prescribed voltage and current range, as well as ensure that the PV array is operated near its maximum power voltage.

• Supply Surge Currents – To supply surge or high peak operating currents to electrical loads.

Page 26: Solar PV Cells, Module and Array

Battery Types & Classification

• Lead-Antimony Batteries

• Lead-Calcium batteries

• Flooded Lead-Calcium, Open Vent

• Flooded Lead-Calcium, Sealed Vent

• Captive Electrolyte Lead-Acid Batteries

Page 27: Solar PV Cells, Module and Array

•Battery Charge (Coulombic) Efficiency : the ratio of Ampere hours withdrawn from a battery during discharge to the Ampere hours provided to re-charge the battery.•State of Charge (SOC) : the amount of energy in a battery at a particular time. Expressed as a %ge of energy stored compared to fully charge battery. •Depth of Discharge (DOD) : %ge of capacity that has been withdrawn compared to fully charged battery. (Depth of discharge and State of Charge adds to 100% of battery) •Allowable depth of discharge : The maximum %ge of full-rated capacity that can be withdrawn from a battery.

Allowable DOD is a seasonal deficit, resulting from low insolation/ temperature and/or excessive load usage. Depending upon the type of batteries used, the designed allowable DOD may be as high as 80%. It is related to autonomy, in terms of capacity required to operate the system loads for a given number of days without energy from the PV array.

Batteries used in PV Systems (Contd.)

Page 28: Solar PV Cells, Module and Array

Balancing the opposites – System design involves compromise between competing and desirable requirements. Choices are to be made between type, size of equipment, location, redundancy, protection, level of safety, amount of complexity, cost etc. Other important factors are client’s budget, remoteness of the site, nature of the load and future growth aspects.

Considerations

Page 29: Solar PV Cells, Module and Array

Considerations (Contd.)

• Required details about PV Application-o Load requirementso Load profileo Surgeso Power qualityo DC or ACo Critical Loadso Ease of access to site.

• Data collection about climate- Latitude, longitudeInsolationTemperatureVariability of weather

• Information about the userBudgetReliability of their dataLevel of technical skillFuture growth possibilitiesAesthetic Considerations

Page 30: Solar PV Cells, Module and Array

System Design Details

Factors involved- • Load characteristic Variation & Estimation• Battery Bank Sizing• Array Sizing• Charge Controller & Wiring Design

• Load – Total daily load demand is calculated by multiplying each load demand times the time that the load operates in a typical 24-hours period. DC loads are estimated by using amp-hours. While AC loads are estimated by using watt-hours.

Page 31: Solar PV Cells, Module and Array

DC Loads Qty Amps Hours /day Daily Demand (Ah)

X XX XX XX XX X

Total DC Loads (Ah)-

Daily Load Form

System Design Details

Page 32: Solar PV Cells, Module and Array

DC Loads Qty Amps Hours /day Daily Demand (Ah)X XX XX X

AC Sub-Total (Wh)

Continuous Watts = _____Surge Est = _____Inverter choice. : ____________________[ ] / [ ] / [ ] + [ ] = ________AC Sub-Total Efficiency Input Voltage DC Loads Daily Load(Ah)

Contd.

System Design Details

Page 33: Solar PV Cells, Module and Array

• Battery Bank Sizing – For this, required parameters are:

– Number of reserve days– Daily Load– Battery Efficiency– Temperature derating– Rate factor– Maximum depth of discharge

Number of days of Reserve x Daily loadBattery Capacity = --------------------------------- Battery Efficiency x Temp.Derate Factor x Rate Factor

System Design Details

Page 34: Solar PV Cells, Module and Array

ARRAY SIZING

Module daily output =Max. peak current(Imp) x sun availability in peak hour

Nominal system voltageNumber of series modules = -----------------------------

Nominal module voltage

Daily load (AH)Number of parallel modules = ---------------------------------------------

Coulombic Efficiency X Module output X Derating factor

System Design Details

Page 35: Solar PV Cells, Module and Array

• Charge Regulator Size –

It is in accordance with the total current from an array which is given by the no of

modules or strings in parallel, multiplied by module short circuit current and

safety factor. The formula is as under.

Regulator Size = No. of parallel modules x Isc x 1.2 (safety factor)

System Design Details

Page 36: Solar PV Cells, Module and Array

The summarized steps:

Step 1- Determination of daily/ weekly/ seasonal total load. Consideration of other key design inputs such as operating voltage, insolation and autonomy.

Step 2- Determination of the battery bank size. This includes battery efficiency,

no.of batteries, battery configuration etc.

Step 3- Selection of solar photovoltaic array, Estimation of maximum current & voltage. Determination of number of modules, module configuration etc.

Step 4- Charge controller selection

System Design Details